The present invention relates to a pusher assembly for an insertion system for a self-expanding vascular implant, wherein the pusher assembly has a catheter tube which has a lumen for accommodating a guide wire and which has a first, proximal catheter tube portion and, adjoining the latter, a second, distal catheter tube portion, wherein the distal catheter tube portion is provided at least partially for movably accommodating a vascular implant thereon, and wherein the catheter tube moreover has a pusher unit for releasing the vascular implant, said pusher unit being proximally adjacent to a vascular implant loaded onto the catheter tube.
Insertion systems for inserting and releasing vascular implants in vessels of a patient, which insertion systems have the aforementioned pusher assembly, are known in the prior art. With insertion systems of this kind, vascular implants, which are also referred to as endovascular stents or stent grafts, for example for treatment of aneurysms or for keeping vessels open, are generally implanted into the vessels to be treated.
The vascular implants presently in use are mainly composed of a hollow cylindrical metal frame, of which the jacket surface is covered by a textile or polymer material, such that a hollow cylindrical body is obtained, which is also referred to as a stent graft or covered stent, whereas braided or laser-cut or twisted metal wire meshes that are not covered about the circumference by a textile or polymer material are referred to as stents or uncovered stents.
For implantation, the vascular implant is radially compressed such that its cross-sectional area is considerably reduced. For introduction into a vessel of a patient, the vascular implant is introduced into the vessel with the aid of an insertion system and released. On account of the spring action of the metal frame, the vascular implant expands back to its original shape after its release and thus spreads open its jacket surface, which clamps itself inside the blood vessel and thereby either bridges the aneurysm or holds the blood vessel open by the spring action. To obtain the desired effect of a vascular implant, it is not only necessary for it to be positioned such that, particularly in the case of an aneurysm, it is able to clamp itself sufficiently firmly in the corresponding blood vessel; the radial orientation of the vascular implant is also often of very great importance. This is particularly the case when further vessels branch off at or near the location where the vascular implant is to be implanted, since the introduction of the vascular implant must not adversely affect the supply to these branches. It is therefore extremely critical, especially at these locations, that the stent is not displaced in its longitudinal direction in the implantation.
For implantation, as has already been mentioned above, the vascular implants are radially compressed and are then positioned in the vessel, in the area thereof to be treated, with the aid of a guide wire, a guide wire catheter, onto which the vascular implant is generally loaded, a pusher rod and a proximal handling portion, and optionally with the aid of further additional known features. The correct position of the vascular implant can be monitored via X-ray markers, for example, which are provided on the guide wire, on the guide wire catheter, on the jacket of the stent, or at other locations.
To ensure that the vascular implants remain in a compressed state during the positioning, they are arranged in a sleeve or a tube that compresses the vascular implant radially inward. After the vascular implant has been positioned in the vessel, this so-called withdrawal sleeve is pulled back and, in order to fix the stent, it is held axially by what is called a pusher, which is arranged in the proximal direction. The pusher lies in contact with the vascular implant and holds the latter in its axial position, while the withdrawal sleeve also surrounding the pusher is pulled away from the vascular implant, which thus expands and clamps itself in the vessel.
At the start of the implantation step, a guide wire is first inserted into the vessel and advanced to the vessel area to be treated. As soon as the vessel area to be treated is reached, the distal part of the insertion device, i.e. the part which lies farther from the operator than the proximal part of the insertion system actuated by the operator and which encloses the guide wire catheter, the vascular implant and the pusher, is guided over the guide wire into the vessel and to the area to be treated. The guide wire catheter is generally provided with a flexible dilator tip at its distal end, in order to widen the vessel paths such that the insertion device and the vascular implant can be more easily received therein.
To ensure that the distal end of the insertion device has a certain degree of flexibility, the guide wire catheter, on which the vascular implant is carried during the insertion into the vessel, is generally flexible, such that this part in particular can adapt to the conditions of the treated vessel, in particular to the curvatures of the latter, and to the guide wire via which the guide wire catheter is inserted.
On the other hand, on account of the high forces that are exerted when pulling the withdrawal sleeve back in order to release the stent, it is necessary that the pusher is generally much stiffer than the guide wire catheter, so as to ensure a sufficiently strong abutment force against the proximally directed force that is exerted during the withdrawal of the withdrawal sleeve that compresses the vascular implant. For these reasons, the pusher is therefore generally much stiffer than the other components of the insertion system.
The withdrawal sleeves normally used in the prior art are generally composed of polymer tubes which are in most cases made from polyethylene or tetrafluoroethylene. The wall thickness of these polymer tubes is dimensioned such that it withstands the expansion pressure of the collapsed vascular implant, remains stable over the course of time and is not subject to any thermal creep. This means, however, that the withdrawal sleeve has a relatively high geometric moment of inertia of its cross-sectional profile. Moreover, withdrawal sleeves are relatively stiff in the axial direction, so that the operator does not lose control of the degree of release of the vascular implant. For these reasons, the pusher should also be stiffer than the withdrawal sleeve in the axial direction, so as to be able to sufficiently counteract the forces described above.
Therefore, the insertion systems known in the prior art generally comprise, in addition to an internal guide wire catheter, also a stiff pusher catheter tube and an outer sleeve tube or sleeve catheter.
It has now been shown that, especially in the case of patients with extremely tortuous vessels, the insertion systems known in the prior art can be used only with difficulty if at all, since the stiffness of the component parts, in particular of the pusher catheter tube, does not allow the insertion system and the vascular implant to be advanced through the tortuous vessels. In addition to the danger of perforation of the vessel wall, there is also the disadvantage that, with the insertion systems known in the prior art, the stent cannot be positioned with sufficient precision in highly tortuous vessels, and also that the withdrawal sleeve buckles, and that this buckling means that greater force has to be applied to overcome the kinks in the withdrawal sleeve. There is also a danger of the guide wire catheter buckling in relation to the pusher catheter tube guided over it, specifically at the transition point to the pusher catheter, and this likewise necessitates the discontinuation of the insertion procedure.